How to PoS mine?
You will mint coins with PoS as long as your wallet is unlocked. To unlock your wallet only for minting, you can enter this command in the Debug Window (Help menu -> Debug window -> Console):
walletpassphrase YOUR_PASSPHRASE 31536000 true
where the number is the length of time (in seconds) to leave the wallet unlocked. Here I set it to 1 year.